The present invention relates to heat treatment fixtures and more particularly, to an improved heat treatment fixture which is constructed in a manner to relieve thermal stresses developed within the fixture during the heat treatment process.
Various metal fabricated parts are heat treated, typically subsequent to machining operations, to modify the physical properties (i.e hardness) of the product. As is well known, the heat treatment process contemplates the placement of the fabricated metal products upon a heat treatment fixture which is inserted into a furnace to raise the temperature of the fabricated part and fixture to a predetermined level within a specific time interval. Subsequently, the fabricated products are cooled or quenched within a predetermined time period to yield the desired physical properties to the prefabricated products.
Heretofore, the majority of the heat treatment fixtures utilized in the prior art have comprised relatively large carts or similar vehicles, typically formed of stainless steel rectangular elongate members which have been rigidly welded and or bolted together in a frame-like network. The lowermost portion of the prior art fixtures have usually included a rigid grid adapted to carry or support the prefabricated parts thereon and have been provided with roller bearing mounted wheels to permit the fixture to be manually inserted and removed (i.e. loaded and unloaded) from the heat treatment furnace. Although such prior art heat treatment fixtures have proven generally suitable in the past, they possess substantial deficiencies which detract from their overall effectiveness in the trade.
Foremost of these deficiencies has been the inability of the prior art heat treatment fixtures to accommodate or withstand the thermal expansion and contraction encountered during the heat treatment process. This inability has caused the prior art heat treatment fixtures to either routinely become warped during prolonged use, thereby hindering the insertion and removal of the same into the heat treatment furnace or in severe instances, has caused the fixture to crack or structurally fail thus preventing the fixture from being further utilized without costly structural repair as by way of cutting and/or welding. Although these thermal expansion problems have been recognized in the art, the solutions to date have comprised the use of heavier structural members and/or the use of stronger rigid weldments or bolt connections on the fixture in an attempt to provide a structure capable of withstanding the thermal expansions.
In addition, due to the prior art heat treatment fixtures typically being formed of relatively heavy stainless steel members, they necessitate a substantial amount of heat energy to be transferred to the same during the heat treatment process, which in many instances, prevents the heat treatment furnace from raising the temperature of the fabricated products to specified tolerances within the required heat treatment time period. As such, the use of the prior art heat treatment fixtures has often resulted in improper heat treatment specifications resulting in a many of prefabricated parts becoming scrapped during the heat treatment process.
Further, in view of the rigid, heavy stainless steel structure of the prior art heat treat fixtures, they have been extremely difficult to manually insert within the heat treat furnace. In addition, such prior art fixtures have typically been expensive to initially purchase as well as subsequently repair, and have failed to provide any mechanism to permit the length and/or volume of the fixture to be modified at the end user's location to adapt the fixture to meet the particular heat treatment production requirements.
As such, there exists a substantial need in the art for an improved heat treatment fixture which is relatively lightweight and economical in use, is capable of withstanding without damage, the thermal expansion encountered during heat treatment process, and which may be rapidly repaired and modified directly in the field to meet the particular heat treatment production requirements.